Reverberation is the ongoing relay of sound after is has been produced. This is naturally created when a sound (or audio signal) is reflected by physical objects, which in turn cause more reflections to occur against one another as the sound is absorbed by things in the sounds environment. It is often added to tracks in audio productions to convey realism and/or for creative effects.
Reverb is not limited to indoor spaces as objects in outdoor environments also provide surfaces for the sound to reflect, although sound will resonate far more prominently in enclosed areas. Sounds or audio signals will gradually decrease in volume and audio amplitude until the sound no longer exists (or reaches zero amplitude).
Reverberation is a naturally occurring physical affect, so it is often added as an audio effect to instruments and recordings to provide life and realism to the track, particularly if the sound is captured in a ‘dry’ space with little reflections. It can also be used to heavily alter audio profiles, which can be manipulated to sound as though it was recorded in a different environment or space. Common examples of this objective would be to make a vocal track sound as though it was performed by the singer in a large concert hall, or make drums sound big and empowering.
Reverb can be applied to recordings in many ways. Historically, reverberation of audio tracks was obtained via re-amping (link) the signal through an amplifier or speaker into a room or chamber with a lot of reflections. This projected signal is then re-recorded and blended with the ‘dry’ track to add space and dimension. Over time, other methods of were created to simplify this process and facilitate more control, the most prominent of these being plate and spring reverbs.
For decades, engineers have been developing digitally controlled devices that use various signal processing algorithms to mimic and create reverb effects. These units are exceptionally popular as it further refines the degree of control for its application. Additionally, digital based reverb can facilitate hundreds of sound and space emulations without taking up a lot of space and can thus streamline workflow and make processing much easier.
A plate reverb uses a transducer to create vibrations within a large plate of sheet metal suspended (or floating) within a frame. The transducer converts a chosen audio signal into an electrical signal to actively create vibrations and movement within the metal plate. The plate’s motion in reaction to these vibrations is recorded up by at least one contact microphones, such as a pickup or a piezo. The audio signal captured by these mics is then mixed with the original ‘dry’ signal.
The reverberation time is adjusted by using a dampening pad, made from framed acoustically designed tiles. The distance of the pad controls the length and shortness of the reverb tail, with smaller gaps creating a shorter reverb time. These plates have to be stored in a quiet room as they are able to pick-up additional background sounds, so remote controls are often used to enable adjustment of the reverb time from a studio control room.
Plate reverbs became most prominent when Elektro-Mess-Technik (EMT) introduced their 140 model. Although weighing in at 600 pounds, this style of reverb was adherently smaller and easier to control that chamber or room reverb spaces. The EMT 140 specifically contributed to many legendary records produced at Abbey Road Studios for The Beatles and Pink Floyd.
Spring reverberation systems work by having a transducer at one end of a metal spring and a pick-up at the other. The transducer converts the chosen audio signal into an electrical signal (and vise versa) to actively create and capture vibrations within the spring with the assistance of the pick-up. Different styles and sizes of springs will alter the effect it has on the audio signal, as will the material used for the casing for the spring (metal, wood etc.).
Spring reverbs are often incorporated into guitar amps because of their compact size, affordability and desirability. Initially, springs weren’t adopted into the professional circuit of the recording industry with their small construction and modest cost being more appealing to semi-professionals or hobbyists with budget restrictions.
Over time, more sonically advanced models of spring reverbs became popular with audio enthusiasts. While springs are generally considered less popular than plate reverbs, there are a few iconic spring reverberation units that are still highly sought after today.
Spring reverb units can also facilitate some pretty nifty creative manipulation. Many musicians have made sound effects with harsh and distorted sounds by rocking or shaking the springs, causing them to produce crashing, thundering sounds as the springs collide with each other. Softer, more gentle movements can also create alternative manipulations of the audio signal.
Chamber and Room Reverb
The first types of reverberations effects created and captured for recording purposes used a physical echo chamber or room. A chosen audio signal is projected into these spaces using loudspeakers, which is then re-recorded to include the effects of reverberating space and blended with the ‘dry’ track to add space and dimension. This technique is still common, although it is mostly used as a creative tool for capturing additional room noise as opposed to using a dedicated room, so other forms or reverb are usually also incorporated.